Shaped woven tubular soft-tissue prostheses and methods of manufacturing

ABSTRACT

Continuously flat-woven implantable tubular prostheses have seamless woven sections which gradually change the number of warp yarns to smoothly transition, i.e., taper, from one diameter to another. Multi-diameter endoluminal grafts having a variety of shapes and configurations are made using a seamless weaving process without unacceptable voids or gaps in the tubular wall.

This application is a divisional of U.S. application Ser. No. 08/653,028filed May 24, 1996, now U.S. Pat. No. 5,800,514.

FIELD OF THE INVENTION

The present invention relates to shaped seamless woven tubularprostheses and methods of manufacture. In particular, the presentinvention relates to implantable endoluminal prostheses used in thevascular system.

BACKGROUND OF THE INVENTION

Tubular woven fabrics have been used for soft-tissue implantableprostheses to replace or repair damaged or diseased lumens in the body.In particular, endoprostheses are used in the vascular system to preventthe blood from rupturing a weakened section of the vessel. Suchendoluminal conduits are generally affixed in a specified location inthe vessel by means of stents, hooks or other mechanisms which serve tosecure the device in place. Endoluminal tubular devices or conduits canalso be used in other lumens in the body, such as in the esophagus andcolon areas.

Vascular grafts have been used successfully for many years to replacesegments of the diseased vessel by open surgical methods. Thesetechniques, however, required long and expensive procedures which have ahigh degree of risk associated with them due to the complexity of thesurgical procedures. Presently, non-invasive techniques for treatingbody lumens, such as vessels in the vascular system, have become moreprominent because they present less risk to the patient and are lesscomplex than open surgery. Generally, a doctor will make an incision inthe femoral artery and introduce an endoluminal device by means of acatheter delivery system to the precise location of the damaged ordiseased vessel. The device will generally include a stent and graftcombination which is deployed from the delivery system and affixed inplace usually by use of a balloon catheter. The balloon catheter is usedto expand the stents which are attached to and most often containedwithin the graft portion. Expansion of the stent serves to both anchorthe graft and to maintain the graft and the body lumen in the openstate. In some cases, self-expanding stents or the like are used. Stentsmade from shaped-memory materials, such as nitinol, are also employedwhereby radial expansion or contraction of the stent is designed tooccur at specified temperatures.

The use of tubular endoluminal prostheses, however, requires a highdegree of precision in the diameter of the tube, such that its externaldiameter matches the internal diameter of the body lumen very closely,thereby conforming to the internal surface of the body lumen. Thevessels or lumens in the body, however, often vary in diameter and shapefrom one length to another, in addition to sometimes defining a tortuouspath therebetween. This is particularly true with the vessels in thevascular system. Thus, tubular endoprostheses which are generallystraight in configuration cannot accurately conform to all portions ofthe lumen which have these variations present. Oftentimes, theprosthesis wall will require a bunching or gathering within the lumen ofthe vessel which presents a long-term potential for thrombosis andgenerally creates a more turbulent environment for blood flow.

More recently, in recognition of certain problems in implanting anddelivering endoluminal prostheses, a thinly woven graft has been madewhich is designed to closely fit the inner lumen of vessels. Such agraft is described in co-assigned and co-pending U.S. Ser. No.08/285,334 filed on Aug. 2, 1994, herein incorporated by reference. Thethinness of this graft allows for it to be easily packed into a catheterdelivery system and occupy less space within the lumen when deployed.However, these grafts have been made in straight lengths or bifurcatedstructures using traditional weaving techniques which have specificlimitations as to the final shape of the product and, in the case ofbifurcated or multi-diameter grafts, the transition from one diameter toanother occurs at a single point in the weave, creating a sudden changein the weaving pattern of the fabric. Such sudden changes, as furtherdiscussed herein, are considered undesirable.

Weaving is commonly employed to fabricate various tubular shapedproducts. For example, implantable tubular prostheses which serve asconduits, such as vascular grafts, esophageal grafts and the like, arecommonly manufactured using tubular weaving techniques, wherein thetubular product is woven as a flat tube. In such weaving processes, avariety of yarns are interwoven to create the tubular fabric. Forexample, a set of warp yarns is used which represents the width of theproduct being woven, and a fill yarn is woven between the warp yarns.The fill yarn is woven along the length of the warp yarns, with eachsuccessive pass of the fill yarn across the warp yarns for each side ofthe tube representing one machine pick. Thus, two machine picksrepresent one filling pick in a tubular woven structure, since weavingone fill yarn along the entire circumference of the tube, i.e., onefilling pick, requires two picks of the weaving machine. As such, in aconventional woven product, the fill yarn is woven along the length ofthe warp yarns for a multiple number of machine picks, with the wovenproduct produced defined in length by the number of filling picks of thefill yarn and defined in width by the number of warp yarns in which thefill yarn is woven therebetween. Such terminology and processes arecommon in the art of textile weaving.

Woven tubular prostheses such as vascular grafts, having tapereddiameter sections or tailored shapes such as those shown in theinventive figures discussed herein, have heretofore not been madewithout requiring manual customization in the form of cutting, splicingand/or tailoring with sutures. Continuous flat-weaving techniques havenot been able to make diameter changes in a gradual manner, having atapered tubular section transitioning from one diameter to anotherdiameter. Instead, diameter changes in the woven product occurinstantaneously, creating a sudden split in the warp yarns. Such asudden split, such as at the crotch section of a bifurcated endoluminalgraft, leaves gaps or voids in the weave at the splitting point. Thus,conventional bifurcated woven grafts have required sewing of the crotchsection in order to insure a fluid-tight character. Such sewing is laborintensive and is generally done manually, thereby introducing thepotential for human error and reliance on the technique of thetechnician.

Furthermore, the prior art techniques of forming tubular shapes haverequired manual cutting and suturing of standard woven tubes to thedesired size and shape. Continuous weaving of tubular grafts to produceseamless gradual diameter transitions in devices has not been previouslyknown. For example, the change from a first diameter to a seconddiameter in a single lumen, straight graft, in a continuous weavingprocess was not attempted due to the aforementioned limitations.Instead, individual grafts of different diameters would be individuallywoven and sutured together to make a continuous tube. The diameterchange required customized cutting to gradually transition from onediameter to another. For example, in the case where a bifurcated grafthaving a 24 mm aortic section and leg sections with different diameters,e.g. 12 mm and 10 mm, the surgeon would manually cut and tailor one ofthe legs of a bifurcated graft which was formed having two equal legsections with the same diameters, and suture a seam along that leg toform a leg of the desired different diameter. This customizationrequired cutting and suturing. Such customization relied heavily on theskill of the physician and resulted in little quality control in thefinal product. Additionally, such grafts could not always be made inadvance for a particular patient, since the requirements for suchcustomization may not be known until the doctor begins the surgery orprocedure of introducing the device into the body. Additionally, aspreviously mentioned, the suture seams take up considerable amounts ofspace when packed into the delivery capsule or other catheter-likedevice designed to deploy the endoluminal prostheses.

There is currently no prior art means to satisfy the variation inrequirements from patient to patient for proper fit of theendoprosthesis. Prior art continuously woven bifurcated grafts not onlysuffered from the gap created at the warp yarn split, but they existedonly with iliac leg portions having equal diameters. If differentdiameter iliac leg portions were required, this would again beaccomplished through customization. One leg would be manually cut-offand another independently formed leg having a different diameter wouldbe sutured on in its place.

Complex shapes, such as tubular "S" shaped or frustoconical shaped wovensections were not even attempted due to the impractibility, intensivelabor and subsequent cost. Such shaped tubes could not practically bewoven using prior art techniques.

In addition to requiring manual sewing steps, sutures used in prior artcustomized grafts create seams which are to be avoided in endoluminalprostheses, particularly because of the space which they take up whentightly packed into a catheter delivery system. Furthermore, such seamscontribute to irregularities in the surface of the graft and potentialweakened areas which are obviously not desirable.

Due to the impracticalities of manufacturing tubular grafts andendoprostheses, straight and bifurcated tubular grafts often requiredcustomization by doctors using cutting and suturing for proper size andshape.

With the present invention, designs are now possible which heretoforehave not been realized. Thus, the weaving of gradually shaped tubulargrafts in a continuous process to create seamless and void-free conduitsfor implantation in the body has heretofore not been possible. Thepresent invention provides a process of producing such grafts, as wellas providing the weaving structure inherent in products formedtherefrom.

SUMMARY OF THE INVENTION

The present invention relates to flat-woven implantable tubularprostheses, and in particular endoluminal grafts, which have beencontinuously woven to form seamless tubular products having gradualchanges in diameter along their length, as well as various shapedtubular sections formed from gradual changes in the number of warp yarnsengaged or disengaged with the fill yarns during the weaving process.Changes in diameter and/or shape are accomplished by gradually engagingand/or disengaging selected warp yarns with the fill yarns in the weavepattern. It has been discovered that such a gradual transition can beaccomplished using electronic jacquard looms controlled by computersoftware. Such engaging and/or disengaging of warp yarns can change thediameter of the tube in a manner which creates a seamless and gradualtransition from one diameter to another. Additionally, such engagementand/or disengagement can be used to create tubular vascular prosthesesand the like which have any number of shapes as depicted and furtherdescribed herein.

Thus, in one embodiment of the present invention there is provided, aflat-woven implantable tubular prosthesis having warp yarns and fillyarns including first and second spaced apart portions which definetherebetween a transition tubular wall extent, the first portion havinga first diameter and the second portion having at least a seconddiameter different from the first diameter. The tubular prosthesisfurther includes a weaving pattern along the transition tubular wallextent, said weaving pattern having a gradual change in the number ofwarp yarns to provide a seamless transition between the first and secondportions.

In another embodiment of the present invention there is provided, aflat-woven implantable tubular prosthesis including first and secondends defining a tubular wall therebetween, with the tubular wallincluding warp yarns and fill yarns. The tubular wall is defined by afirst elongate woven section with a first selected number of warp yarnstherealong to define a first tubular internal diameter, and a secondelongate woven section seamlessly contiguous with the first wovensection and having a gradual change in the number of warp yarnstherealong to define at least a second tubular internal diameter.

In an alternative embodiment of the present invention, there isprovided, a flat-woven tubular implantable prosthesis having warp yarnsand fill yarns including first and second ends defining a tubular walltherebetween, with the tubular wall having a first woven extent with afirst selected number of warp yarns therealong to define a first tubularinternal diameter, a transitional second woven extent contiguous withthe first woven section with at least a second selected number of warpyarns therealong to define at least a second tubular internal diameterwhich is different from the first tubular internal diameter, and atleast a third woven extent contiguous with the second woven extent witha third selected number of warp yarns which is different from the firstand said second selected number of warp yarns, with the third wovenextent defining a third tubular internal diameter which is differentfrom the first and second tubular internal diameters.

Additionally, methods of forming such endoluminal prostheses are alsoprovided. In one of such methods, there is provided a method of forminga seamless flat-woven implantable tubular prosthesis including the stepsof weaving a tubular wall having transitional diameter along alongitudinal extent thereof, such weaving including gradually engagingor disengaging additional warp yarns along the extent to transition froma first diameter to a second diameter different from the first diameter.

Another embodiment of the methods of the present invention includes amethod of making a seamless flat-woven implantable tubular prosthesisincluding weaving a first section of the prosthesis having a firstdiameter using a first selected number of warp yarns, and transitioningto a second section of the prosthesis having a second diameter differentfrom the first diameter by gradually engaging or disengaging warp yarns.

Additionally included in the present invention is a method of forming aflat-woven synthetic tubular implantable prostheses having a precisepre-determined internal diameter (D) including the steps of: (i)choosing a desired weave pattern; (ii) providing a desired yarn and yarnsize for the weaving pattern; (iii) providing a desired density (ρ) atwhich the yarn is to be woven; (iv) providing a number of warp yarns (S)required to weave a suitable tubing edge; (v) choosing a desiredinternal diameter (D) of the tubular prosthesis; (vi) calculating thetotal number of warp yarns (N) required to weave the tubular prosthesishaving the internal diameter (D) using the formula:

    N=S+(D×ρ)

wherein N represents the total number of warp yarns required, Srepresents the number of warp yarns required to weave a suitable tubingedge, D represents the desired internal diameter and ρ represents thenumber of warp yarns per unit of diameter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a, 1b and 1c depict perspective views of a graft constructed inaccordance with the prior art.

FIGS. 2, 3, 4, 5, 6 and 7 depict perspective views of shaped graftsconstructed in accordance with various embodiments of the presentinvention.

FIG. 8 is a perspective view of a graft of the present invention havinga first diameter tapering to a second diameter shown in a flat, radiallycompressed form after weaving but prior to heat setting.

FIG. 9 is a cross-sectional view of the graft shown in FIG. 8.

FIG. 10 is a cross-sectional view of the graft of FIG. 8 after heatsetting.

FIGS. 11a and 11b are perspective views of weave patterns in accordancewith the present invention.

FIG. 12 is a perspective view of grafts being continuously flat-woven inaccordance with the present invention, showing warp yarns graduallydisengaged from the weave during weaving of one of the graft sections.

FIG. 13 shows a photomicrograph of the internal woven portion of acrotch section of a bifurcated graft of the prior art at a magnificationof 10×.

FIG. 14 shows a photomicrograph of the internal portion of a crotchsection of a bifurcated graft made in accordance with the presentinvention at a magnification of 10×.

FIGS. 15, 16 and 17 depict perspective views of bifurcated graftsconstructed in accordance with alternative embodiments of the presentinvention.

FIG. 18 depicts a perspective view of a trifurcated graft constructed inaccordance with an alternative embodiment of the present invention.

FIG. 19 shows a scanning electron micrograph of the internal portion ofa crotch section of a bifurcated graft of the prior art at amagnification of 30×.

FIG. 20 shows a scanning electron micrograph of the internal portion ofthe crotch section of a bifurcated graft made in accordance with thepresent invention at a magnification of 45×.

FIG. 21 is a perspective view of a bifurcated graft of the presentinvention shown in a flat, radially compressed form after weaving, butprior to heat-setting.

FIG. 22 is a cross-sectional view of the graft shown in FIG. 21.

FIG. 23 is a cross-sectional view of the graft of FIG. 21 after heatsetting.

FIG. 24 is a perspective view of bifurcated grafts being continuouslyseamlessly flat-woven in accordance with the present invention, showingwarp yarns gradually disengaged from the weave during weaving of theiliac sections.

FIG. 25 is a perspective view of bifurcated grafts being continuouslyseamlessly flat-woven in accordance with the present invention, showingwarp yarns gradually disengaged from the weave during weaving of theaortic section.

FIG. 26 is a perspective view of the bifurcated graft of FIG. 17 used inconnection with the tapered graft of FIG. 5, with an internal stentshown at one portion of the graft.

FIG. 27 is a perspective view of the bifurcated graft of FIG. 17including an internal stent extending therethrough.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

It has been discovered through the present invention that tubular woventextile products such as vascular grafts can be seamlessly woven into avariety of shapes and sizes, without the need for any post-weavingfabrication techniques such as cutting, sewing, suturing and the like.

A recurrent problem and limitation in prior art techniques of tubularweaving can be evidenced through the prior art techniques formanufacturing split grafts, such as bifurcated grafts, trifurcatedgrafts, and the like. A split graft consists of a tubular graft sectionof a certain diameter, which splits at a crotch area into a plurality oftubular graft sections or members of a different diameter than the firstgraft section. For example, a bifurcated graft, as depicted in FIG. 15,includes an aortic woven portion 620 with a crotch 627, and splits intofirst and second iliac woven portions 630a and 630b. For the purposes ofthe present invention, split grafts are designated as having a firstgraft section referred to as an aortic woven portion and second graftsections referred to as iliac woven portions or iliac leg sections,since in preferred embodiments, such split grafts, i.e. bifurcatedgrafts, are meant for implantation within the aorta at the branch of theiliac arteries, for instance, for use in repairing an aortic aneurism.

In conventional manufacturing processes for tubular weaving ofbifurcated grafts, it was necessary to split the number of warp yarns atthe crotch area during the weaving process in order to split the tubularwoven graft from the first aortic woven portion 620 into the first andsecond iliac woven portions 630a and 630b. This splitting of warp yarnswas necessary in order to accomplish the transition at the crotch 627,where the diameter of the graft transitions from a first inner diameterof the aortic woven portion 620 to two separate inner diametersrepresenting the first and second iliac woven portions 630a and 630b. Inprior art processes, however, such transition in split grafts from afirst diameter to two equal second diameters was accomplished bysplitting the warp yarns evenly at the crotch 627 during the weavingprocess. It is known that it is desired to us an odd number of warpyarns in order to form a continuous plain weave pattern for tubularweaving. Thus, such splitting of the number of warp yarns in half at thecrotch area in order to form iliac leg portions in prior art processesresulted in an incorrect number of warp yarns in one of the iliac legportions, since the number of warp yarns required in the tubular weavingof the aortic portion was of an odd number, and splitting this oddnumber in half results in an odd number and an even number. Thus, inprior art processes, at least one of the iliac leg portions of a tubularwoven graft often included an incorrect weave pattern at the flat-wovenedge.

In an effort to correct this problem resulting in the wrong number ofwarp yarns in one of the iliac leg portions, the present inventorsdiscovered that it is possible to disengage a warp yarn from the weavepattern for that portion of the weaving process required to weave theiliac leg portions without deleterious effects. In the prior art weavingprocesses the number of warp yarns generally remained constantthroughout the weaving pattern, due to the inefficiencies andimpracticability of disengaging a warp yarn for only a portion of theweaving pattern. The present invention utilizes specially designedsoftware and a customized electronic tubular weaving machine fordisengaging a warp yarn for a portion or portions of the weavingpattern. Thus, by disengaging one warp yarn from the weave pattern atthe crotch area during the weaving process, an odd number of warp yarnscould be utilized during the weaving of the iliac leg sections of thegraft, and the correct weave pattern would be produced throughout theentire graft.

As previously discussed, a further problem with prior art processes inthe manufacture of tubular woven grafts related to achieving precisediameters of the graft. Oftentimes, the portion of a damaged bloodvessel to be repaired included a taper or diameter change, wherein theblood vessel changes from one diameter to a second diameter over thearea to be repaired. In the prior art, in order to compensate for suchchanges in diameters, a surgeon commonly cuts a seamless tubular wovengraft along its length, as demonstrated in FIGS. 1a, 1b and 1c. In FIG.1a, a seamless tubular woven graft 10' is depicted, having a first end12' and a second end 14', with an internal diameter extending throughthe tubular graft. As shown in FIG. 1b, a cut in the wall of the graftwas made, leaving cut edges 13'. Thereafter, the cut edges 13' weresutured together by a surgeon with edge sutures 15', thereby providing atubular woven graft 10' with one diameter at first end 12' whichgradually tapers to a second diameter at second end 14' by way of taperseam 16'. Such a tapering process, however, involved a post-fabricationtechnique, resulting in a tubular woven graft which was no longerseamless and required additional steps after fabrication of the graft.

In order to overcome these problems, the present inventor discoveredthat such a tubular-woven graft could be tapered during the weavingprocess, producing a seamless tubular-woven graft having a taperedconfiguration, as well as a variety of other tapers, flares, and shapesas shown in FIGS. 2 through 7.

With reference to FIG. 2, a typical seamless tubular-woven textile graft10 in accordance with the present invention is shown generally as atapered graft in a generally frustoconical shape. Graft 10 is a textileproduct formed of a woven synthetic fabric. Graft 10 is depicted in oneembodiment in FIG. 2 which includes a generally tubular body 17 having afirst end 12 and an opposed second end 14, defining therebetween aninner lumen 18 which permits passage of blood once graft 10 is implantedin the body. Graft 10 includes continuous transitional woven portion 25extending between first end 12 and second end 14, and extending alongthe entire length of graft 10. Graft 10 of FIG. 2 has a generallyfrustoconical shape, with first end 12 having a first tubular innerdiameter and second end 14 having a second tubular inner diameter whichis different than the inner diameter of first end 12. For example, firstend 12 may have an inner diameter of 12 millimeters and second end 14may have an inner diameter of 10 millimeters, with transitional wovenportion 25 forming a gradual taper having successive changes in diameterthroughout such that graft 10 gradually tapers from the 12 millimeterinner diameter of first end 12 to the 10 millimeter inner diameter ofsecond end 14 along the length of transitional woven portion 25. Thegradual tapering of transitional woven portion 25 is accomplished bygradually disengaging and/or engaging a selected number of warp yarnsfrom the weaving pattern during weaving of the graft, as will bediscussed in more detail herein.

FIGS. 3, 4, 5, 6 and 7 show various shapes of grafts that can be formedaccording to the present invention. FIG. 3 shows a variation of theconfiguration of FIG. 2, with graft 100 in the form of a step-taperedgraft having a tubular body 117 with a first end 112 and an opposedsecond end 114 defining an inner lumen 118 therebetween. In theembodiment of FIG. 3, graft 100 includes first woven portion 120 whichdefines a portion of tubular wall 117 having a continuous first innerdiameter and second woven portion 130 which defines a portion of tubularwall 117 having a continuous second inner diameter which is differentthan the inner diameter of first woven portion 120. Graft 100 of FIG. 3further includes transitional woven portion 125 adjacent and contiguouswith first and second woven portions 120 and 130. In such an embodiment,graft 100 includes a constant diameter extending through first wovenportion 120 and a constant diameter which is different than the innerdiameter of first woven portion 120 which extends through second wovenportion 130, and gradually tapers from the inner diameter of first wovenportion 120 to the inner diameter of second woven portion 130 throughthe length of transitional woven portion 125.

FIG. 4 shows a further variation on the step-tapered configuration ofFIG. 3, with graft 200 having a tubular body 217 with a first end 212and an opposed second end 214 defining an inner lumen 218 therebetween.In the embodiment of FIG. 4, graft 200 includes a first woven portion220 and a transitional woven portion 225, with the first woven portion220 defining first end 212 and including a continuous inner diameteralong the length thereof, and the transitional woven portion 225defining second end 214 and including a gradual taper such that graft200 gradually tapers from the inner diameter of first woven portion 220to a second diameter at second end 214 which is different than the innerdiameter of first woven portion 220. It is contemplated that suchgradual tapering can be either an inward taper or an outward taper(flared).

FIG. 5 shows a further variation on the configuration of graft 10 ofFIG. 2, with graft 300 having a tubular body 317 with a first end 312and an opposed second end 314 defining an inner lumen 318 therebetween.In the embodiment of FIG. 5, graft 300 includes a transitional wovenportion 325 and a second woven portion 330, with the transitional wovenportion 325 defining first end 312 and the second woven portion 330including a continuous inner diameter along the length thereof, anddefining second end 314. Further, transitional woven portion 325includes a gradual taper such that graft 300 gradually tapers outwardlyfrom the inner diameter of first end 312 to a second diameter at secondend 314 which is different than the inner diameter of first end 312.

FIGS. 6 and 7 show further shapes which can be formed according to thepresent invention. FIG. 6 depicts a sinusoidal shaped graft 400 having atubular body 417 with a first end 412 and an opposed second end 414defining an inner lumen 418 therebetween. In the embodiment of FIG. 6,graft 400 includes a continuous first woven portion 420, with the firstwoven portion 420 defining both first and second ends 412 and 414. Firstwoven portion 420 has a continuous inner diameter along the lengththereof, such that first end 412 and second end 414 have the same innerdiameter. Graft 400 is shaped along its length in an "S" configuration,with tubular body 417 gradually changing direction as warp yarns on oneedge of graft 400 during the weaving process are engaged or disengagedwhile the same portion of tubular body 417 on the other edge of graft400 equally changes in the same direction as warp yarns are engaged ordisengaged at this edge. Thus, as warp yarns at one edge of the graftare disengaged as that edge and shape of the graft gradually curves, thecorresponding warp yarns at the opposite edge on the same pick areengaged. As the "S" shape again changes direction, the opposite may betrue, i.e., warp yarns at a given pick on one edge may be engaging ascorresponding warp yarns at the other edge on the same pick may bedisengaging. In order to maintain a constant diameter, the warp yarns ateach of the edges of the tubular graft must simultaneously change byadditionally adding or engaging an equal number of warp yarns on oneedge as the other edge loses or disengages warps. Thus, the total numberof warp yarns within the tubular wall remains constant during theweaving process.

FIG. 7 depicts a variation of the sinusoidal shaped graft 400 shown inFIG. 6. Graft 500 in FIG. 7 includes a tubular body 517 with a first end512 and an opposed second end 514 defining an inner lumen 518therebetween. In the embodiment of FIG. 7, graft 500 includes firstwoven portion 520 having a first inner diameter and second woven portion530 having a second inner diameter which is different than the innerdiameter of first woven portion 520. Graft 500 further includestransitional woven portion 525 adjacent first and second woven portions520 and 530. For example, first woven portion 520 may include a wovengraft section having an inner diameter of 12 millimeters and secondwoven portion 530 may include a woven graft section having an innerdiameter of 10 millimeters, with transitional woven portion 525 forminga gradual taper such that graft 500 gradually tapers from the 12millimeter inner diameter of first woven portion 520 to the 10millimeter inner diameter of second woven portion 530 along the lengthof transitional woven portion 525. Graft 500 is shaped along its lengthin an "S" configuration similar to the manner in FIG. 6, with tubularbody 517 gradually tapering in on one side of graft 500 during theweaving process while the same portion of tubular body 517 on the otherside of graft 500 tapers outwardly.

While a variety of shapes and configurations are shown in the drawingsand described herein, any seamless tubular flat-woven graftincorporating a gradual transitional continuously woven portion iscontemplated by the present invention. The gradual tapering of thetransitional woven portion is accomplished in each of the inventiveembodiments by gradually disengaging and/or engaging a selected numberof warp yarns from the weaving pattern during weaving of the graft, aswill be discussed in more detail herein.

Through the present invention it is now possible to accomplishdisengaging and/or engaging of selected warp yarns to create gradualchanges with size, shape or configuration of the graft during weaving ofthe graft. It has been discovered through the present invention,however, that such disengaging and/or engaging of the warp yarns must beaccomplished in a gradual transition in order to prevent holes or voidsbetween the contiguous sections of the woven graft. It is known that adelicate balance exists between porosity of the graft for properingrowth and the need in many applications for fluid-tight walls. It hasbeen determined that a void greater than the diameter of about threewarp yarns results in a graft with a porosity which is unacceptable as afluid-tight conduit and may be incapable of sufficiently maintainingblood pressure therein. Thus, the transition from a graft section of onediameter to a graft section of another diameter must be accomplished influid-tight applications without creating such voids between thecontiguous weave sections which are generally greater than the diameterof three warp yarns. In applications where fluid-tight walls are notcrucial, the size of such voids may of course be greater.

Any type of textile product can be used as the warp yarns and fill yarnsof the present invention. Of particular usefulness in forming the wovenprostheses of the present invention are synthetic materials such asthermoplastic polymers. Thermoplastic yarns suitable for use in thepresent invention include, but are not limited to, polyesters,polypropylenes, polyethylenes, polyurethanes andpolytetrafluoroethylenes. The yarns may be of the monofilament,multifilament, or spun type.

The yarns used in forming the woven grafts of the present invention maybe flat, twisted or textured, and may have high, low or moderateshrinkage properties. Additionally, the yarn type and yarn denier can beselected to meet specific properties desired for the prosthesis, such asporosity, flexibility and compliance. The yarn denier represents thelinear density of the yarn (number of grams mass divided by 9,000 metersof length). Thus, a yarn with a small denier would correspond to a veryfine yarn whereas a yarn with a larger denier, e.g., 1000, wouldcorrespond to a heavy yarn. The yarns used with the present inventionmay have a denier from about 20 to about 1000, preferably from about 40to about 300. Preferably, the warp and fill yarns are polyester, andmost preferably the warp and fill yarns are one ply, 50 denier, 48filament flat polyester.

The graft of the present invention can be woven using any known weavepattern in the art, including, simple weaves, basket weaves, twillweaves, velour weaves and the like, and is preferably woven using a flatplain tubular weave pattern, most preferably with about 170-190 warpyarns (ends) per inch per layer and about 86-90 fill yarns (picks) perinch per layer. The wall thickness of the graft may be any conventionaluseful thickness, but is preferably no greater than about 0.16 mm, withthe most preferable wall thickness being from about 0.07 mm to about0.14 mm. These thicknesses facilitate the folding of the graft into anappropriate delivery system. Moreover, the seamless (i.e., sutureless)feature of the present invention further facilitates packing and foldingof the graft into the delivery system.

As noted, transition from one diameter to another diameter isaccomplished by gradually engaging and/or disengaging selected warpyarns from the weave pattern. In the present invention, it has beendiscovered that such a transition can be effectively accomplished byengaging or disengaging a maximum of three warp yarns per foursuccessive machine picks for a given weave pattern on each edge of thegraft. Such disengaging or engaging of warp yarns can be accomplished inany combination of numbers. For example, up to three warp yarns can bedisengaged or engaged at any of the four successive machine picks, aslong as the total number of warp yarns engaged and/or disengaged doesnot exceed a maximum of three warp yarns per four machine picks on eachedge of the tubular flat-woven product. An edge is defined as an outerlimit of the graft width as taken along the longitudinal axis as thegraft is flat-woven on the loom. FIG. 8 shows such edges at 117c. Aspreviously noted, two machine picks represents one filling pick oftubular fabric, i.e., one tubular fill yarn. Thus, four machine picksrepresents two tubular fill yarns.

As noted above, preferably the tubular-woven graft of the presentinvention is constructed of polyester which is capable of shrinkingduring a heat set process. For instance, such grafts are typicallyflat-woven in a tubular form. Due to the nature of the flat-weavingprocess, the tubular graft is generally flat in shape after weaving, asdepicted in FIG. 8, which shows a graft 100 in one embodiment of thepresent invention as flat-woven in a tubular step-tapered form as shownin FIG. 3. As shown in cross-sectional view in FIG. 9, such a flat-woventubular graft subsequent to weaving is generally elliptical in shape.Such grafts, however, when constructed of heat-settable polyester yarn,can be heat set on a mandrel to form a generally circular shape, asdepicted in FIG. 10.

Such a heat setting process is accomplished by first flat-weaving thegraft in a tubular form out of a material capable of shrinking during aheat setting process. After the graft is woven, the graft is placed on amandrel, and heated in an oven at a temperature and time capable ofcausing the yarns of the graft to heat set to the shape and diameter ofthe mandrel. Preferably polyester yarns are used as the warp and fillyarns, and the heat setting is accomplished at time and temperaturesappropriate for the material. For example, heat setting can beaccomplished at about 190-200° C. for a period of about 14-16 minutes.Other methods of heat setting known in the art may be employed. Aftersuch a heat setting process, the graft can be formed into a shapedesired for implantation, having a generally circular inner lumen.

As noted above, due to the nature of the flat-weaving process, whilegraft 100 is tubular, it is generally flat in shape during weaving andprior to the aforementioned heat setting, as shown in FIG. 9. Thepost-fabrication flat shape of tubular wall 117 is comprised of toptubular body portion 117a and bottom tubular body portion 117b, whichconnect at tubular body edges 117c. While reference has been made to aheat setting process for forming graft 100 into a generally cylindricalshape as shown in FIG. 10, graft 100 can be provided as a finishedproduct in the generally flat shape shown in FIG. 9, or can be madecylindrical in shape by any known methods. Further, crimping of thegraft 100 along the length of tubular wall 117 to provide structuralintegrity is contemplated.

FIG. 11a shows a conventional plain tubular weave pattern known in theart. Warp yarns 160 are further shown as 160a indicating they are in thetop layer of the weave and 160b indicating their presence in the bottomlayer of the weave. Top warp yarns 160a and bottom warp yarns 160b runin a lengthwise direction in the graft and define the width of thegraft. Fill yarns 170 are further shown as top fill yarns 170a andbottom fill yarns 170b. These fill yarns are woven with the top andbottom warp yarns 160a and 160b as shown in FIG. 11a in a manner knownin the art. For example, a filling yarn shuttle (not shown) passesacross warp yarns 160 while selected warp yarns 160 are lifted accordingto a specific weave pattern. In electronic weaving machines, such weavepatterns can be programmed using software into the machine. In a typicalplain tubular weave as depicted in FIG. 11a, the shuttle first weavestop fill yarn 170a by passing across warp yarns 160 while certain warpyarns 160 are lifted. During travel of top fill yarns 170a (direction X)for weaving of the top tubular body portion such as top tubular bodyportion 117a of graft 100, the bottom warp yarns 160b are not lifted toprevent top fill yarns 170a from interweaving with bottom warp yarns160b. Likewise, during passage of bottom fill yarns 170b (direction Y)for weaving of the bottom tubular body portion such as the bottomtubular body portion 117b of graft 100, the top warp yarns 160a arealways lifted such that bottom fill yarns 170b are not interwoven withtop warp yarns 160a. The plain tubular weave pattern as just describedcan be used to form straight portions of the inventive grafts which havea constant diameter. This pattern is then modified by gradually engagingor disengaging warp yarns to create tapers and/or shapes.

For example, the plain weave pattern shown in FIG. 11a and describedabove is formed by continuously passing top and bottom fill yarns 170aand 170b back and forth across warp yarns 160 to form first wovenportion 120 of graft 100 shown in FIG. 12.

FIG. 11b shows a plain tubular weave pattern having a gradualdisengaging of warp yarns. As seen in FIG. 11b, warp yarns 160' havebeen disengaged from the pattern and are no longer interwoven beginningat the fill yarn 170'. Likewise, the next set of picks shows anadditional warp yarn being disengaged. As noted, the pattern is withinthe maximum disengagement of three warp yarns per four machine picks.

The disengaging of the warp yarns is accomplished by dropping thedesired warp yarns from the end of the tubular flat-woven graft duringthe weaving process, such that the fill yarns are not interwoven acrossthe warp yarns for that section of the pattern. Such dropping of warpyarns in a gradual manner forms the transitional portion of the graft.In continuous flat-weaving processes, the warp yarns are then re-engagedduring the weave pattern once the transitional section has beencompleted. Once the complete graft has been woven, the weave pattern maybe repeated creating the next graft to be woven in a continuous process.

FIG. 12 shows a plurality of grafts 100 being woven in a continuousflat-weaving process, in accordance with the present invention. Firstwoven portion 120 is of one inner diameter, for instance 24 millimeters,while second woven portion 130 is of another inner diameter differentthan that of first woven portion 120, for instance 18 millimeters. Assuch, first woven portion 120 requires more warp yarns 160 for weavingthan does second woven portion 130. Thus, at transitional portion 125,the warp yarns are gradually disengaged from the weave, as depicted bydisengaged warp yarns 160'. Since the grafts of the present inventionare preferably fabricated using a continuous flat-weaving process,disengaged warp yarns 160' must be re-engaged into the weave patternafter completion of the second woven portion in order to begin weavingthe first woven portion of the subsequent graft to be produced. Throughsuch a continuous flat-weaving process, a plurality of grafts 100 can bewoven in a continuous manner, and can be cut apart along line C afterfabrication. Furthermore, disengaged warp yarns 160' are removedsubsequent to weaving.

For flat-weaving of bifurcated tubular grafts, prior art processestypically involved splitting of the warp yarns in half at the portion ofthe weave pattern where the graft splits from the aortic graft portionto the iliac leg portions, with the iliac leg sections of the grafttherefore being woven with half the number of warp yarns as the aorticsection of the graft. With such techniques, however, variations in thediameters of the iliac leg sections could not be accomplished in aseamless manner. Typically, when a tubular woven bifurcated graft withtwo different diameter iliac leg portions was required, i.e., when atubular woven bifurcated graft having iliac leg portions with diametersdifferent than that which would be formed by splitting the number ofwarp yarns in half was desired, the bifurcated graft would have to befirst woven in a conventional manner, followed by cutting and suturingof the iliac to achieve the desired diameter. As discussed above, graftsproduced in such a manner resulted in many drawbacks. For instance, thesuture seam added to the wall thickness of the graft and added adiscontinuity to the internal wall surface of the graft. Further, graftsrequiring such post-fabrication suturing resulted in voids in the graftwall from the needle which was used for suturing. FIG. 13 shows aphotomicrograph of an enlarged view of the internal portion of a priorart bifurcated graft woven of warp yarns 161 and fill yarns 171 at thecrotch area 627' of the graft, where the two iliac leg portions branchoff from the aortic portion. Needle holes 140 are present in the wall ofthe graft, representing holes through the graft wall which were made bya needle during suturing of the iliac leg portions to the aorticportion.

Through the present invention, split grafts such as bifurcated graftscan be flat-woven in a tubular form with varying diameters in the iliacportions and the aortic portion, without the need for suchpost-fabrication suturing. This is accomplished by a gradual transitionin the number of warp yarns in the weave of the graft, as accomplishedin the tapered grafts discussed above. Such gradual transition isaccomplished by gradually engaging or disengaging warp yarns during thefabrication of the graft at the transition from the aortic graft portionto the iliac leg portions of the graft. A bifurcated graft produced inthis manner is shown in an enlarged view at FIG. 14. FIG. 14 shows abifurcated graft having first and second iliac woven portions 630a and630b. As compared with the prior art graft shown in FIG. 13, the needleholes 140 which were created from the suturing needle required forattachment of the iliac legs in the prior art grafts are not present inthe graft produced in accordance with the present invention.

Referring generally to FIG. 15, a typical tubular woven bifurcated graft600 includes a generally tubular body 617 having a first end 612 andopposed second ends 614a and 614b, defining therebetween an inner lumen618 which permits passage of blood once bifurcated graft 600 isimplanted in a blood vessel. Bifurcated graft 600 includes aortic wovenportion 620 having a first inner diameter, and further includes firstand second iliac woven tubular wall portions 630a and 630b each havingan inner diameter which is different than the inner diameter of aorticwoven portion 620. The inner diameters of first and second iliac wovenportions 630a and 630b can be the same, as depicted in FIG. 15, or canbe different, as depicted in 730a and 730b of FIG. 16. Further, iliacwoven portions 630a and 630b can be of the same general length as shownin FIGS. 15 and 16, or can be of different general lengths, as shown at830a and 830b in FIG. 17. Bifurcated graft 600 further includesbifurcated transitional woven portion 625 contiguous with aortic wovenportion 620 and first and second iliac woven portions 630a and 630b atcrotch 627 forming a bifurcated arch. Bifurcated transitional wovenportion 625 forms a gradual taper such that bifurcated graft 600gradually tapers from the inner diameter of aortic woven portion 620 tothe inner diameters of first and second iliac woven portions 630a and630b along the length of bifurcated transitional woven portion 625. Thegradual tapering of bifurcated transitional woven portion 625 isaccomplished by gradually disengaging and/or engaging a selected numberof warp yarns from the weaving pattern during weaving of the graft, asaccomplished in the preferred embodiment discussed above.

FIG. 18 depicts a trifurcated graft 900 in accordance with analternative embodiment of the present invention. Trifurcated graft 900is of the same general configuration as bifurcated graft 600 shown inFIG. 17, including a generally tubular body 917 having first end 912,second ends 914a, 914b and 914c with first woven portion 920,transitional woven portion 925, first and second iliac woven portions930a and 930b, and further includes an additional iliac leg as iliacwoven portion 930c. Further, trifurcated graft 900 also includescrotches 927a, 927b and 927c (not shown), extending between transitionalwoven portion 925 and each of iliac woven portions 930a, 930b and 930c.

Prior art processes for tubular weaving of split grafts such asbifurcated and trifurcated grafts and the like resulted in holes orvoids in the crotch area of the grafts, which in certain applicationsfurther resulted in undesirable porosity for the graft. The porosity ofgrafts is of vital importance, since such grafts are to be implantedinto the body as fluid conduits and therefore must be of a porositywhich prevents undesirable fluid leakage through the wall of the graft.The voids which were formed in the crotch area of bifurcated graftsproduced by the prior art tubular weaving techniques resulted in highporosity of the graft at the crotch area and required suturing beforethey were acceptable for implantation. A bifurcated graft woven of warpyarns 161 and fill yarns 171 having such reinforcement sutures isdepicted in FIG. 19, representing the prior art. FIG. 19 is a scanningelectron micrograph of a prior art bifurcated graft showing the crotcharea in an enlarged view. Warp yarns 161 and fill yarns 171 are seengenerally in the micrograph. Crotch sutures 150 are shown, whichundesirably create an added area of wall thickness in the graft.

The present inventor has discovered that such voids in the crotch areaof a split graft can be avoided by gradually transferring the warp yarnsduring the weaving process from one woven section to another wovensection contiguous thereto, thereby avoiding the necessity forpost-fabrication suturing of voids. Thus, as depicted in FIG. 20, aclosed weave is established in crotch 627 of a bifurcated graft 600, bygradually transferring the warp yarns during the weaving process fromone woven section to another woven section contiguous therewith.

For example, during weaving of the bifurcated graft 600, as shown inFIG. 15, the warp yarns 160 which are being interwoven by the fill yarns170 are gradually transferred from the aortic woven section 620 and thetransitional woven section 625 to each of the iliac woven portions 630aand 630b.

Further, during weaving of bifurcated graft 600, two separate fillingyarn shuttles (not shown) are required for weaving of the two distinctiliac woven portions 630a and 630b. To form the gradual transition inthe crotch 627 avoiding holes, the shuttle designated for weaving ofiliac woven portion 630a selectively and gradually engages warp yarnsdesignated for weaving of iliac woven portion 630b. Likewise, theshuttle designated for weaving iliac woven portion 630b selectively andgradually engages warp yarns designated for weaving of iliac wovenportion 630a. In this manner, the crotch 627 is woven using asimultaneous tapering effect at the interface between the aortic wovenportion 620 and iliac woven portions 630a and 630b. As such, a smoothcontiguous surface transition is obtained.

When weaving materials for implantation such as vascular grafts,however, it is necessary to provide exact inner diameters for the wovengrafts. It has been discovered that, when using heat setting yarns suchas polyester for the weaving yarns, the actual diameter after heatsetting of the yarns is not easily predictable using conventionaltechniques. For example, in the prior art weaving of a tubularbifurcated graft having an aortic graft section of 26 millimeter innerdiameter and two iliac leg sections of 13 millimeter inner diameter, thewarp yarns were split in half in order to weave the iliac leg sections,with 627 warp yarns required for weaving of the aortic graft section,and 313 warp yarns (half of 627) being used for weaving of each of theiliac leg sections. When such a graft was flat-woven of polyester intubular form and then heat set, however, the exact diameters of 26millimeters for the aortic section and 13 millimeters for each of theiliac leg sections was not accomplished. Although the aortic sectionachieved the 26 millimeter diameter, the iliac leg portions shrunk to asmaller diameter than 13 millimeters, making the graft difficult toremove from the mandrel. Thus, the graft was not a true 26×13×13 set ofdiameters.

As noted above, the invention employs customized, programmableelectronic jacquard weaving machines to gradually engage and/ordisengage selected warp yarns from the weaving pattern during weaving ofa flat-woven tubular product. With such capabilities, the presentinventor has discovered that the number of warp yarns required for eachof the tubular segments having different diameters can be pre-determinedto account for the variation in heat shrinkage from one diameter to thenext. Thus, in yet another alternate embodiment of the presentinvention, a method of forming a flat-woven synthetic tubularimplantable prosthesis having a precise pre-determined internal diameteris provided. In the method, a desired weaving pattern is first selectedfor constructing the prosthesis. Preferably, the weaving pattern isselected from the group consisting of a simple weave (plain weave), abasket weave, a twill weave, and velour weaves. A desired yarn size andyarn diameter is then provided for the weaving pattern. The density atwhich the yarn is to be woven in the weave is then chosen, representedby a specific number of warp yarns per unit diameter. Additionally, aselected number of warp yarns is provided for weaving a suitable tubingedge. The desired internal diameter of the tubular prosthesis is thenselected. Based upon knowing these parameters, the total number of warpyarns required to weave the tubular prosthesis with such a desiredinternal diameter can be calculated using the following formula:

    N=S+(D×ρ)

wherein N represents the total number of warp yarns required, Srepresents the number of edge warp yarns required to weave a suitabletubing edge , D represents the desired internal diameter and ρrepresents the number of warp yarns per unit of diameter. By applyingthe aforementioned steps, it has been discovered that an exact innerdiameter for a given synthetic tubular woven product can bepredetermined to account for variation in shrinkage due to heat setting.In a preferred embodiment, S is 29 when the diameter D is an evennumber, and S is 28 when the diameter is an odd number. In such apreferred embodiment, the density ρ is 23 using a 1 ply/50 denier/48filament polyester yarn.

Turning now to FIGS. 21-23, bifurcated graft 600 of FIG. 21 is depictedin a generally flat tubular shape subsequent to weaving, with toptubular wall portion 617a and bottom tubular wall portion 617bconnecting at tubular edges 617c in a similar means as graft 100,previously discussed with relation to FIGS. 8-10.

Further, FIGS. 24 and 25 show a plurality of bifurcated grafts 600 beingwoven in a continuous flat-weaving process, in accordance with oneembodiment of the present invention. Bifurcated grafts 600, as shown inFIGS. 24 and 25, are woven in a similar manner as grafts 100, depictedin FIG. 12. In FIG. 24, however, bifurcated graft 600 includes aorticwoven portion 620 and first and second iliac woven portions 630a and630b, with aortic woven portion 620 requiring more warp yarns forweaving than the iliac woven portions 630a and 630b. As such, duringweaving of the iliac woven portions 630a and 630b, selected warp yarnsare gradually disengaged from the weave at transitional woven portion625 as represented by disengaged warp yarns 660'. In FIG. 25, iliacwoven portions 630a and 630b require more warp yarns for weaving thanaortic woven portion 620, and thus the disengaged warp yarns 660' aredisengaged during weaving of the aortic woven section.

The tubular prostheses formed in accordance with the present inventioncan be used in surgical procedures as well as non-invasive procedures.Alternatively, the tubular prostheses of the present invention can beused in conjunction with a variety of stents in order to maintain theprostheses within the lumen of the body to be repaired. For example,FIG. 26 shows a bifurcated graft in accordance with one embodiment ofthe present invention, including a stent 50 affixed thereto at oneportion of bifurcated graft. FIG. 27 shows a bifurcated graft inaccordance with an alternative embodiment of the present invention,having stent 50 substantially along the entire length of tubular wall617, positioned within the inner lumen of bifurcated graft. Such a stent50 is well known in the art, and can be constructed in any desired shapeand of any material known in the art, for example, a shaped memoryalloy, as disclosed in International Application No. PCT/US95/01466,incorporated herein by reference. It is contemplated by the presentinvention that stent 50, as well as other stent types, can be used insuch a manner with any of the tubular woven grafts of the presentinvention.

EXAMPLES

Unless otherwise noted, the grafts of all of the following examples wereflat-woven in a tubular configuration using an electronic jacquardweaving machine. All of the grafts were flat-woven using a plain tubularweave pattern. The warp yarns and the fill yarns were constructed ofsingle ply, 50 denier, 48 filament polyester with 170-190 warp ends perinch per layer and 86-90 fill yarns per inch per layer.

Example 1

The purpose of Examples 1 and 2 are to demonstrate that even when theelectronic jacquard loom is used, unless the gradual engagement ordisengagement of warp yarns is employed in accordance with the presentinvention, acceptable void free grafts will not be obtained.

A stepped graft (no taper) was flat-woven on an electronic jacquard loomin a tubular configuration to produce a 12 millimeter inner diametersection of the graft and a 10 millimeter inner diameter portion of thegraft. The number of warp yarns required for weaving the 12 millimeterinner diameter portion of the graft was calculated using theabove-mentioned method for pre-determining the number of warp yarnsrequired to achieve the true desired diameters upon heat shrinking asfollows:

    N=S+(D×ρ)

    N=29+(12×23)

    N=305

The number of warp yarns required for weaving the 10 millimeter innerdiameter portion of the graft was similarly calculated as follows:

    N=29+(10×23)

    N=259

The 12 millimeter inner diameter portion of the graft was firstflat-woven to a desired length. During the flat-weaving process, 46 warpyarns were disengaged from the weaving pattern all at once, i.e., at asingle machine pick, in order to produce the 10 millimeter innerdiameter portion of the graft. The graft thus produced included a 12millimeter inner diameter portion and a 10 millimeter inner diameterportion. The transition between the two portions, however, includedlarge holes between the weave sections of the graft which were visibleto the naked eye.

Example 2

A graft having a 12 millimeter inner diameter portion and a 10millimeter inner diameter portion was flat-woven in a manner similar tothat of Example 1. During the transition from the 12 millimeter innerdiameter portion to the 10 millimeter inner diameter portion, however,all 46 warp yarns were not disengaged at once transitioning to the 10millimeter diameter portion. Instead, 4 or more warp yarns weredisengaged for every 2 machine picks. The graft thus produced included a12 millimeter inner diameter portion and a 10 millimeter inner diameterportion. The transition between the two portions, however, also includedunacceptable holes between the weave sections of the graft which werevisible to the naked eye.

Example 3

This example demonstrates the requirement for a maximum of three warpyarns which can be engaged or disengaged for every 4 machine picks. Agraft having a 12 millimeter inner diameter portion and a 10 millimeterinner diameter portion was flat-woven in a manner similar to that ofExample 2. During the transition from the 12 millimeter inner diameterportion to the 10 millimeter inner diameter portion, either 1 or 2 warpyarns were disengaged for every 4 machine picks, with a maximum of 3warp yarns being disengaged for every 4 machine picks. The graft thusproduced included a 12 millimeter inner diameter portion and a 10millimeter inner diameter portion. The transition between the twoportions included a gradual transition with no holes between the weavesections of the graft.

Example 4

This example demonstrates than the selection of the number of warp yarnsfor each desired diameter of a bifurcated graft must be made using theinventive method steps in order to obtain the true desired diameters andaccount for variation in heat shrinkage. A set of bifurcated grafts wereflat-woven in a tubular configuration to produce an aortic sectionhaving a 24, 26 and 28 millimeter inner diameter and two iliac legsections having a 12, 13 and 14 millimeter inner diameter for each legsection, respectively. The aortic section of the grafts were firstflat-woven. When the weave reached the bifurcation portion, thepreviously described inventive method of gradually changing the warpswas not employed. Instead, the number of warp yarns were split all atonce, i.e., at a given pick, with one warp yarn being disengaged asnecessary for one leg of the iliac leg section in order to produce thecorrect weave pattern (obtain an odd warp yarn number). The number ofwarp yarns used for each graft is shown in Tables 1-3.

None of the number of warp yarns for the aortic or the iliac sectionswere determined using the aforementioned inventive method, and as such,none of the warp yarn numbers were calculated in accordance with theformula stated therein.

                  TABLE 1    ______________________________________    NUMBER OF WARP     NUMBER OF WARP    YARNS USED FOR     YARNS USED FOR    24 mm AORTIC SECTION                       EACH 12 mm ILIAC SECTION    ______________________________________    Graft 1A           583             291    Graft 1B           587             293    Graft 1C           591             295    Graft 1D           595             297    ______________________________________

                  TABLE 2    ______________________________________    NUMBER OF WARP     NUMBER OF WARP    YARNS USED FOR     YARNS USED FOR    26 mm AORTIC SECTION                       EACH 13 mm ILIAC SECTION    ______________________________________    Graft 2A           657             313    Graft 2B           631             315    Graft 2C           635             317    Graft 2D           639             319    ______________________________________

                  TABLE 3    ______________________________________    NUMBER OF WARP     NUMBER OF WARP    YARNS USED FOR     YARNS USED FOR    28 mm AORTIC SECTION                       EACH 14 mm ILIAC SECTION    ______________________________________    Graft 3A           675             337    Graft 3B           679             339    Graft 3C           683             341    Graft 3D           687             343    ______________________________________

After the grafts were woven, they were placed on steel mandrels and heatset in an oven for a sufficient time and temperature to heat-set theirshapes and size, i.e., at a temperature of 190-200°0 C. for 14-16minutes. After removing the grafts from the mandrels, the aortic sectionof each of the grafts was properly heat set to an inner diameter of 24,26 and 28 millimeters. The iliac leg sections, however, were heat settoo tightly on the mandrels, making it difficult to remove the legsections from the mandrels. The actual inner diameter of each of theiliac leg sections was less than the desired 12, 13 and 14 millimeters,respectively.

Example 5

The following example demonstrates the use of the inventive method offorming a bifurcated graft of a desired diameter. This invention alsoshows, however, that when the rate of changing (disengaging or engaging)the warp yarns is greater than 3 warp yarns per 4 machine, unacceptablevoids are present in the weave.

A set of bifurcated grafts were flat-woven in a tubular configuration ina similar manner as in Example 4, to produce an aortic section having a24, 26 and 28 millimeter inner diameter and two iliac leg sectionshaving a 12, 13 and 14 millimeter inner diameter for each leg section,respectively. The aortic section of the grafts were first flat-woven.When the weave reached the bifurcation portion, the number of warp yarnswas adjusted by disengaging warp yarns from the weave pattern at a rateof 4 warp yarns being disengaged for every 4 machine picks. The totalnumber of warp yarns used for each graft was calculated by the formulaas described herein.

    N=S+(D×ρ)

The calculated warp yarn numbers for each diameter section is set forthin the tables below.

                  TABLE 4    ______________________________________    NUMBER OF WARP     NUMBER OF WARP    YARNS USED FOR     YARNS USED FOR    24 mm AORTIC SECTION                       EACH 12 mm ILIAC SECTION    ______________________________________    Graft 4           581             305    ______________________________________

                  TABLE 5    ______________________________________    NUMBER OF WARP     NUMBER OF WARP    YARNS USED FOR     YARNS USED FOR    26 mm AORTIC SECTION                       EACH 13 mm ILIAC SECTION    ______________________________________    Graft 5           627             327    ______________________________________

                  TABLE 6    ______________________________________    NUMBER OF WARP     NUMBER OF WARP    YARNS USED FOR     YARNS USED FOR    28 mm AORTIC SECTION                       EACH 14 mm ILIAC SECTION    ______________________________________    Graft 6           673             351    ______________________________________

After the grafts were woven, they were placed on steel mandrels and heatset in an oven at a temperature of 190-200° C. for 14-16 minutes. Afterremoving the grafts from the mandrels, the aortic section of each of thegrafts was properly heat set to an inner diameter of 24, 26 and 28millimeters, respectively. The iliac leg sections were also properlyheat set to an inner diameter of 12, 13 and 14 millimeters,respectively. When the disengaged warp yarns were removed from theexterior portion of the aortic graft section, however, holes visible tothe naked eye were present in the tubular wall of the graft at thetransition between the aortic portion and the iliac leg portions.

Example 6

This example demonstrates the use of the inventive embodiment, i.e.,using gradually disengaged warp yarns to transition from the aorticsection to the iliac sections, and the use of the inventive method ofcalculating the number of warp yarns required for a given diameter.

A set of bifurcated grafts were flat-woven in a tubular configuration inthe same manner as in Example 5, to produce an aortic section having a24, 26 and 28 millimeter inner diameter and two iliac leg sectionshaving a 12, 13 and 14 millimeter inner diameter for each leg section,respectively. When the weave reached the bifurcation portion, however,the number of warp yarns was adjusted by disengaging warp yarns from theweave pattern at a rate of no more than 3 warp yarns being disengagedfor every 4 machine picks. After the grafts were woven, they were heatset in the same manner as in Example 5. After removing the grafts fromthe mandrels, the inner diameters of the aortic section of each of thegrafts measured 24, 26 and 28 millimeters, respectively, and diametersof the iliac leg sections measured 12, 13 and 14 millimeters,respectively. The precise desired inner diameters were thus obtainedusing the inventive method of determining the proper number of warpyarns necessary to account for heat set shrinkage. Moreover, when thedisengaged warp yarns were subsequently removed from the exteriorportion of the aortic graft section, no holes were present in thetubular wall of the graft at the transition between the aortic portionand the iliac leg portions. This clearly demonstrates the necessity forthe gradual change in warp yarns as claimed herein.

The invention being thus described, it will now be evident to thoseskilled in the art that the same may be varied in many ways. Suchvariations are not to be regarded as a departure from the spirit andscope of the invention and all such modifications are intended to beincluded within the scope of the following claims.

What is claimed is:
 1. A method of forming a flat-woven synthetictubular implantable prosthesis having a precise pre-determined internaldiameter (D) and a predetermined degree of blood tightness comprisingthe steps of:(i) selecting a desired weaving pattern and weaving type;(ii) providing a plurality of yarns having a predetermined yarn size;(iii) determining a yarn density (ρ) at which said plurality of yarnsare to be woven to yield said predetermined blood tightness; (iv)determining a number of edge warp yarns (S) required to maintain saiddesired density (ρ) at a suitable tubing edge; (v) defining a desiredinternal diameter (D) of said tubular prosthesis; (vi) weaving saidtubular prothesis having a total number (N) of said plurality of warpyarns in said warp direction using the formula:

    N=S+(D×ρ)

wherein N represents the total number of warp yarns required, Srepresents the number of edge warp yarns required to weave a suitabletubing edge, D represents the desired internal diameter and ρ representsthe number of warp yarns per unit of diameter.
 2. The method of claim 1wherein said weaving type is selected from the group consisting of aplain weave, a basket weave, a twill weave, and velour weave.
 3. Themethod of claim 1 wherein said yarn is 1 ply, 50 denier, 48 filamentpolyester yarn.
 4. The method of claim 3 wherein said density (ρ) is 23.5. The method of claim 4 wherein said number of edge warp yarns (S) is29 when said diameter (D) is an even number and 28 wherein said diameter(D) is an odd number.